The rapid expansion of the world's population coupled with the accelerated technological development of large sectors of the world has produced a dramatic increase in the demand for energy in all forms including fuels and electricity for heating, lighting, transportation and manufacturing processes. The construction of hydroelectric facilities and the development of fossil fuel resources has continued at a rapid rate but it becomes increasingly evident that these efforts are inadequate to keep pace with the demands of the growing population.
Until recently, the development of solar energy collectors for commercial use has been largely directed to the flat plate collector which is made of metal and glass with one or more layers of glass laid over a blackened plate. Air spaces are provided between layers of glass and air or water passes through these tubes under the metal plate to remove the collected energy. The layers of glass in cooperation with the blackened plate act as a heat trap, letting in the sun's rays but keeping most of the heat from escaping again.
A major disadvantage of the flat plate collector is that it must be very large in order to collect sufficient energy, the large size resulting in part from the fact that except for brief periods during the day its surface is not perpendicular to the rays of the sun.